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Mineralogical and Physical Characterization of Some Clayey Soils
from Parts of Southwestern Nigeria for Ceramic Application.
Yinusa Ayodele Asiwaju-bello1, Sunday Olabisi Daramola1*, Joshua Oluwasanmi Owoseni1, Oluwaseun
Franklin Olabode1,2, Victor Oladoja3, Raymond Oluwadolapo Aderoju4, Kunle Barnabas Oladapo1, and
Ayodeji Aderibigbe5
1Department of Applied Geology, School of Earth and Mineral Sciences, Federal University of
Technology, Akure, Nigeria
2Department of Geology & Geophysics, School of Geosciences, University of Aberdeen,
Aberdeen, Scotland (UK)
3Department of Earth Sciences, College of Liberal Arts and Sciences, University of Connecticut, USA
4Department of Geology, Franklin College of Arts and Sciences, University of Georgia, Athens, USA
5John A. Reif, Jr. Department of Civil and Environmental Engineering, College of Engineering, New
Jersey Institute of Technology, Newark, USA
*Corresponding Author
DOI: https://dx.doi.org/10.51584/IJRIAS.2025.101100082
Received: 11 November 2025; Accepted: 18 November 2025; Published: 19 December 2025
ABSTRACT
Clayey soils have long been utilized in various industrial applications, particularly in the production of ceramics.
The physical and mineralogical properties of these soils control their intrinsic behavior, which plays a vital role
in determining their suitability for industrial applications. This study aims to explore the mineralogical and
physical properties of selected clayey soils from Ekiti state in southwestern Nigeria and assess their implications
for ceramic applications. The XRD analysis revealed that the soils contain kaolinite and illite as the dominant
clay minerals, with significant quantities of quartz as well as considerable percentages of muscovite and goethite.
Physical tests indicate that the soils consist of clays, silts, sand, and a subordinate amount of gravels, while the
range of clay-sized particles suggests that the soils would not exhibit excessive shrinkage during firing. The
plasticity chart reveals that the soils plot in the domain of medium to high plasticity and compressibility.
Additionally, most of the clays studied presented liquid limit values in the range defined for raw clayey materials
designated for ceramic applications. Moreover, the plasticity index of the clayey soils suggests that they are
unlikely to be susceptible to inappropriate extrusion process. The position plots of the clayey soils on the
workability chart indicate that the linear shrinkage of these samples would require some amendments prior to
their processing. Furthermore, the high linear shrinkage exhibited by the soils could result in deformation and
microcracking during the production of bricks, thereby requiring the addition of degreasers to reduce the
plasticity of the clays before utilization. A general reduction in the water adsorption capacity with a
corresponding increase in the firing temperature was observed. This could significantly affect the durability and
mechanical characteristics of the soils. The flexural strength (FS) of the studied soils generally increased with
increased firing temperature suggesting that the technological property is highly dependent on the temperature
of firing.
Keyword: ceramic, clayey soils, flexural strength, kaolinite, plasticity
INTRODUCTION
The utilization of clayey soils in ceramic production dates back to ancient civilizations, where their unique
properties were harnessed to produce durable and functional ceramic goods. The different notable applications
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of clayey soils in various industries, particularly in ceramics, underscore the importance of understanding their
geological and chemical properties. The intrinsic properties of these soils are influenced by their mineralogical
and physical characteristics, which play a critical role in determining their suitability for ceramic manufacturing
(Bomeni et al., 2018; Ohandja et al., 2020; Nweke et al, 2023). These soils are primarily composed of clay
minerals such as kaolinite, illite, and montmorillonite, which influence their plasticity, strength, and firing
characteristics (Ntouala et al., 2016; Ohandja et al., 2020; Oumar et al., 2022). Thus, a comprehensive
understanding of the mineralogical composition of these soils is essential for enhancing their performance in
ceramic applications. Hence, detailed studies of clay mineralogy, including the types and proportions of clay
minerals present, are essential for ensuring that these materials meet the specific requirements of ceramic
production. The diverse nature of the rock types in the study area contributes to a variety of clayey soil types,
which have been historically used in traditional ceramic production. Hence, characterizing these clayey soils is
crucial for optimizing their suitability for various ceramic applications, including tiles, pottery, and bricks.
However, despite the potential, there is limited comprehensive research on the properties of notable clayey soils
in Ekiti State. Previous studies have often focused on broader geological surveys without a detailed analysis of
the clay's suitability for ceramics. This research aims to fill this gap by providing a thorough characterization of
clayey soils from parts of Ekiti State, focusing on their mineralogical composition, physical properties, and
geotechnical behaviour. This is with a view to ascertaining the quality and applicability of these clays for ceramic
use by analyzing their mineralogy, plasticity, drying and firing shrinkage, and thermal properties. By employing
a range of analytical techniques, including X-ray diffraction (XRD), physical, and technological analysis, this
research seeks to provide a comprehensive understanding of the clayey soils and their potential for industrial
applications. Understanding these properties will not only contribute to the optimization of ceramic products but
also foster sustainable local industries by utilizing indigenous raw materials. Ultimately, this research intends to
support the development of a robust ceramics industry in Ekiti State, leveraging local clay resources to meet
both domestic and international market demands.
METHODS
2.1 Study area
The study area is part of Ekiti State in southwestern part of Nigeria (Figure 1). It lies between Latitude 70301 and
70801North of the Equator, and Longitude 40961E and 50601 East of the Greenwich Meridian. It is located in the
humid tropical part of South-western Nigeria with distinct dry and wet seasons. The study area is principally an
upland region rising over 400 m above sea level with an undulating terrain and a typical landscape that comprises
old plain separated by steep-sided outcrops occurring singularly or in groups or ridges (Talabi, 2013). The
dendritic drainage pattern dominates the area (Figure 1), implying that the underlying rocks are to a large extent
uniformly resistant to weathering. The area is well drained by notable rivers such as Elemi, Ogbese, Ose, Ureje,
and their system of tributaries, and the main rivers that drain the area flow southwards (Ayodele, 2022).
Figure 1: Topographic and drainage map of Ekiti State
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Ekiti State is located within a major part of the Precambrian basement complex of Nigeria (Figure 2), which
forms part of the Pan-African belt and is flanked by the Congo and West African Cratons (Talabi et al., 2018).
Oyinloye (1998) noted that the rocks of the basement complex were formed as a consequence of four orogenic
events, namely, the Liberian (2700 Ma), the Eburnean (2000 Ma), the Kibaran (1100 Ma), and the Pan-African
cycle (600 Ma). The Liberian, Eburnean, and Kibaran events were typified by strong deformations with
associated regional metamorphism that was later followed by migmatisation. The Pan-African cycle (600 Ma)
was accompanied by regional metamorphism, migmatisation, extensive granitization, and gneissification. This
resulted in the formation of homogeneous gneisses and syntectonic granites (Rahaman and Ocan, 1978). Late
tectonic emplacement of granodiorites, granites, and contact metamorphism complemented the final phases of
this latter deformation. Olayinka (1992) noted that fracturing and faulting marked the end of the Pan-African
orogeny. Ekiti state is predominantly underlain by Precambrian crystalline rocks of igneous and metamorphic
origin (Rahaman and Ocan, 1978; Talabi and Tijani, 2013; Oyelami and Van Rooy, 2018). The notable rock types
in the study area are charnockite, Pan African granite, schists with pegmatite, quartzites, and migmatite (Figure
2).
Figure 2: Geological Map of the study area
2.2 Sampling and Laboratory Analysis
The samples were obtained from the representative clay bodies widely distributed in different parts of the study
area (Table 1). The mineralogical analysis of the clay soil samples was undertaken by utilizing the Bruker D8
Advance diffractometer equipped with an automated multi-position flip-stick sample stage. Samples were
analyzed using the standard open polystyrene sample holder in θ–θ configuration with a Goebel mirror, exit slit,
and anti-divergent slit with Nickel-filtered Copper radiation (λ = 1.5506 Å). The identification of the qualitative
phase was conducted through the application of the Search/ Match method, where the measured diffraction peak
(peak positions and intensities) is matched against the ICDD (International Center for Diffraction Data) PDF-4+
2021 database entries by employing the software + Sieve. Quantification of the phases was carried out using the
Rietveld refinement method (TOPAS v6 software). The particle size analyses were conducted in accordance with
the specification of the British Standard Institution (BSI, 1990) by using wet sieving and hydrometer analysis
(sedimentometry) methods for particles of size ≥ 80 and ≤ 80 μm respectively. An electric shaker was used for
the sieve method, while the sedimentometry was based on the principle of Stokes’ law of sedimentation of
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individual spherical particles falling freely at a steady velocity under the influence of gravity. The liquid Limit
(LL) was measured with the Casagrande dish and the Plastic Limit (PL) by the roller method, all according to
ASTM D4318 – 2005 standard. Plasticity Index was calculated by the arithmetic difference between LL and PL.
Firing was done in a muffle furnace of FP34G type, with a maximum temperature of 1100 °C. The tested
specimens were subjected to five firing temperatures: 800 °C, 900 °C, 1000 °C, and 1100 °C. The water
absorption (WA), expressed as a percentage of the weight relationship water absorbed after soaking in water for
24 h to the weight of the dry specimen (ASTM C20, 2000). WA was calculated as:
1
where W2 is the weight of soaked specimen and W1 weight of dry specimen. The loss on ignition was determined
by the same formula of water absorption. Here, W2 is the weight of dry specimen, and W1 represents the weight
of the firing specimen. The flexural strength in MPa was calculated for each specimen using equation 2 (ASTM
F417, 1996):
2
where P is the load at fracture (N), L= distance between supporting knife edge (50 mm), l is the width of the
specimen, and h represents the thickness of specimen (mm). The data derived from the raw materials fired at
varying temperatures were characterized and compared with standard specifications.
Table 1: Location and description of the clayey soil samples from the study area.
Sample Name
Coordinates
Sampling depth
(cm)
Extension
Latitude (N)
Longitude (E)
Ire-1
7° 42ʹ 10.6ʺ
05° 24ʹ 14.2ʺ
102
Ire-3
7° 42ʹ 10.6ʺ
05° 24ʹ 14.2ʺ
124
Ire-2
7° 45ʹ 59.32ʺ
05° 23ʹ 44.36ʺ
130
507m²
Isan-1
7° 56ʹ 04.6ʺ
05° 20ʹ 20.1ʺ
63
564m²
Isan-2
7° 55ʹ 36.3ʺ
05° 19ʹ 28.8ʺ
164
647m²
Ara-2
7° 46ʹ 00.1ʺ
05° 06ʹ 41.0ʺ
337
445m²
Ara-3
7° 46ʹ 00.1ʺ
05° 06ʹ 41.0ʺ
624
RESULTS AND DISCUSSION
3.1 Mineralogy
Typical X-ray diffractogram of the studied soils are presented in Figures 3a and 3b, while the quantitative
proportions of the minerals identified are presented in Table 2. It could be observed that kaolinite and illite are
the dominant clay minerals, while quartz and goethite are the non-clay minerals identified in the soils. The
ceramic properties of clays depend on the content of the clay minerals, specifically the illite/smectite minerals,
and crystallinity of kaolinite and illite (Baioumy et al, 2014). These features influence the grain size distribution
and specific surface area of the clays. Hence, optimal clays for ceramic applications should contain higher
amounts of low-ordered kaolinite and illite and some amounts of illite-smectite (I/S) minerals. Thus, the studied
clays are characterized by an abundance of clay fractions as well as kaolinite and illite, while no smectite
minerals were detected. These properties suggest the suitability of the studied clays as good-quality raw materials
for ceramic applications. Furthermore, the significant occurrence of illite suggests that the clay soils could be
widely utilized as fluxing materials in traditional ceramics for the production of cooking pots, stoneware tiles,
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and bricks (Ferrari and Gualtieri, 2006). Furthermore, the occurrence of quartz as the dominant non-clay mineral
in the soils would enhance the strength of ceramics, thereby influencing the quality of the end products.
Figure 3a: Typical X-ray diffraction patterns of the clayey soils (Ara-2) analyzed for the study area
Figure 3b: Typical X-ray diffraction patterns of the clayey soils (Ire-2) analyzed for the study area
Table 2: Mineralogical composition of the clayey soils sampled from the study area
Sample code
Kaolinite
Illite
Quartz
Goethite
Ire-1
34.5
0.0
0.0
65.5
Ire-3
12.5
13.6
73.9
0.0
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Ire-2
9.0
0.0
91.0
0.0
Isan-1
47.4
52.6
0.0
0.0
Isan-2
79.4
20.6
0.0
0.0
Ara-2
16.3
11.2
72.4
0.0
Ara-3
22.2
0.0
77.8
0.0
3.2 Physical
The distribution of the particle sizes of clayey materials plays a prominent role in the determination of their
suitability for ceramic applications with particular attention being given to the clay fractions (finer than 2µm).
Celic (2010) noted that the particle size influences their technological behavior, particularly the drying and firing
processes, thereby affecting several properties of the clay products, such as the mechanical properties of the fired
materials. The grain size distribution characteristics of the studied clays, as revealed by the particle size analysis
are shown in Figure 4, while the proportions of the different particle sizes are presented in Table 3.
Figure 4: Ternary diagram classification of the studied clay materials
Table 3: Physical parameters of the clayey soils from the study area
Sample
No.
Grading (%)
Specific
Gravity
Atterberg Limits
Plasticity
Linear
Shrinkage
(%)
<0.075
mm
Clay
0.002-
0.02µm
<0.02µ
m
>20µ
m
Liquid
Limit
(%)
Plastic
Limit
(%)
Plasticity
Index
(%)
Ire-1
33.6
5.2
3.1
8.3
91.7
2.6
52.2
30.4
21.9
MH
20.0
Ire-3
76.0
26.0
28.3
54.3
45.7
2.5
75.3
38.1
37.1
MH
10.7
Ire -2
64.1
19.1
21.5
40.5
59.5
2.6
95.0
60.1
34.9
MH
13.6
Isan1
47.4
14.0
28.0
42.0
58.0
2.6
69.9
27.3
42.6
CH
8.6
Isan2
53.1
19.0
24.3
43.3
56.7
2.7
37.3
18.3
19.0
CI
10.7
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Ara-2
74.5
15.8
30.8
46.6
53.4
2.6
41.1
13.8
27.3
CI
17.9
Ara-3
96.1
23.1
41.3
64.4
35.6
2.6
72.1
41.8
30.2
MH
16.4
Figure 5. Position plots of the soils on a suitability diagram
It could be observed that the soils consist of particle sizes ranging from clays, silts, sand, and subordinate amount
of gravels. Clay size particles range from 5.2 to 26% with some variations observed with depth, as the samples
obtained at greater depth presented a higher amount of clay give a reason. Thus, the range of clay-sized particles
(finer than 2µm) suggests that the raw materials would not exhibit excessive shrinkage during firing, as raw
materials with finer fractions greater than 80% often cause excessive shrinkage during firing. Furthermore, the
sample from Ara contains higher clay size fractions with an average value of 19.45%. Also, the average value of
the clay fractions is within the range obtained by Ferari & Gualtieri (2006) for clays from Turkey. According to
Diko et al (2011), suitable clay materials designated for ceramic applications are commonly classified as silty
clay, sandy clays, clayey silt, and loam. Based on the sand-silt-clay ratios, a classification of the studied soils
using the ternary diagram of Shepard (1954) presented in Figure 5 reveals that the studied soils are largely sandy
silty with isan-1 and ara-2 classifying as silty sand and clayey silt respectively. The plot of the clays on the
Winkler’s diagram (Figure 6) indicates that the studied clay soils are suitable for utilization as common bricks,
perforated bricks, roofing tiles, and masonry bricks. However, Ire-1 may require amendment before use.
Figure 6. Grain size classification of the soils according to the Winkler diagram. A=common bricks; B=
vertically perforated bricks; C= roofing tiles and masonry bricks; D=hollow products.
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The atterberg limits of soils are important parameters in the evaluation of clay soils for ceramic applications as
they control their behavior and workability. The results of the atterberg limits reported in Table 3 indicate that
the liquid limits range from 37.3 to 95%, plastic limit range from 13.8 to 60.1% while the plasticity index ranges
from 19 to 42.6%. The plasticity chart (Figure 7) reveals that the soil plots in the domain of medium to high
plasticity and compressibility. Previous studies (e.g., Daoudi et al. 2014, Daramola et al 2018) indicated that
plasticity of clayey materials is essentially controlled by grain size distribution, mineralogical composition, and
the occurrence of organic matter. Thus, the range of plastic limit is closely related to the values specified for
kaolinite and illite Nweke et al 2023. The soils show plastic limit value which indicates the minimum moisture
content necessary to reach a plastic condition. Although soil samples are more difficult to dry at high plastic
limit, the use of high plastic clays reduces the wearing down of the equipment for grinding and conformation
(extruder) (Celik, 2010; Oyebanjo et al 2020, Nweke et al 2023). Furthermore, most of the clays studied
presented liquid limit values in the range defined by different researchers (eg Baccour et al, 2009; Semizand and
Celik 2020) for raw clayey materials designated for ceramic applications.
Figure 7. Position of the clayey soil samples on Casagrande plasticity chart.
Moreover, raw materials with low plasticity index (≤10) are considered inappropriate for use in the production
of ceramics related to building sometimes usually requires the addition of a polymer so as to achieve adequate
plastic behavior and to avoid an inappropriate extrusion process related to cracking during extrusion (Boukoffa
et al, 2021; Nweke et al, 2023). On this basis, the plasticity index presented by the clayey soils under
consideration are generally greater than 18.97% indicating that they are unlikely to be susceptible to
inappropriate extrusion process. Furthermore, the projection of the clays studied on the workability chart is
presented in Figure 8. It could be observed that some of the samples exhibit acceptable and optimal molding
properties except for Ire-2, Ire-3, Ara-2, and Isa-3. The workability chart (Figure 8) further indicates that the
linear shrinkage of these samples (Ire-2, Ire-3, Ara-2, and Isa-3) would require some property improvements
prior to their processing. In addition, due to the risk of sticky consistency, Ire-2 and Isa-3 may also require
amendment as they exhibit a significantly high plasticity index. The activity values obtained for the clayey soils
are generally greater than 0.75, which suggests that the soils are active (Bell, 2007). This could be attributed to
the presence of illite clay minerals, which are generally considered essential for improving the plasticity of raw
materials and for forming the location of vitreous phases during firing, thereby improving the strength and
densification of the ceramic bodies (Nweke et al., 2023). Thus, the presence of illite significantly enhanced the
plasticity behavior of the studied clayey soils and would likely influence the firing strength and drying behavior
of the final products. The linear shrinkage values of the clayey soils range from 8.6 to 20% with an average of
13% which fails to conform to the range of 7 to 10% specified for fired clays (Diko et al., 2020). The fairly high
linear shrinkage values can be attributed to the amount of clays and the occurrence of illite (reference). Moreover,
the high linear shrinkage values are inimical to its application for tiles production as minimal shrinkage during
the firing of raw materials for ceramic production is vital (Garcia-Valles et al., 2020). Furthermore, the high
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linear shrinkage could result in deformation and microcracking during the production of bricks, thereby requiring
the addition of degreasers to reduce the plasticity of the clays before utilization.
Figure 8. Plots of the clayey soils on the workability chart based on their plasticity characteristics
(DikoMakia and Ligege, 2020)
3.3 Technological Properties
The results in Figure 9 show that the water absorption capacity ranges from 15.4 to 39% when fired at 850oC
and ranges from 10.44 to 15.42 % when fired at 1100oC. The plots of the variations in the water absorption
capacity with firing temperature (Figure 9). Reveals a general reduction in the water adsorption capacity with a
corresponding increase in the firing temperature. This could be attributed to the combustion of organic matter,
decarbonation and dehydration reaction (Ngun et al., 2011). This could significantly affect the durability and
mechanical characteristics of the raw materials thereby transforming them into more resistant and more durable
materials. Also, the reduction in the water adsorption capacity could be attributed to the glassy phase formation
that penetrates into pores closing them and isolating them from the neighboring pores (Lambering 1993;
Kagombe et al., 2021). Although, the average values of the water adsorption capacity of the soils fired at 1100oC
conforms to the maximum limit <25%and <20% specified by Souza (2002) for dense brick and roofing tiles
respectively. However, the water adsorption capacity of some samples are quite higher than the standard specified
thus rendering them unsuitable for such applications. Furthermore, the range of water adsorption capacity at
1000oC agree with the range (8.03 to 24.27%) specified for quality and process control parameters in the
development and manufacturing stages to produce structural ceramics.
The loss on ignition (LOI) is a very important property that reveals the quantity of organic matter present in the
raw materials and further reveals the extent of vacuum and the percentage of water absorption (Nweke et al.,
2023). The LOI ranged from 13 to 22% at 800°C, while at a higher temperature of about 900°C, it ranged from
16 to 27% after which the values of the LOI remained constant (Figure 10). On a general note, the increase in
LOI as the firing temperature increased from 800 to 900oC may be due to the elimination of organic matter by
combustion, loss of structural water, decomposition of some minerals such as clay minerals and sulphate during
firing (Bauluz et al., 2004; Tsozue et al., 2017; Kagonbe et al., 2021).
The flexural strength (FS) of the studied soils are presented in Figure 11. It shows a general increase with
increasing firing temperature. This further suggests that the technological property is highly dependent on the
temperature of firing. The presence of illite in the soils may have significantly influenced the flexural strength
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of the studied clay samples after firing. Furthermore, the flexural strength values of the studied clayey soils at
1000°C are significantly lower than those earlier reported by Dondi et al. (2002) for Italian brick clays, as well
as other authors such as Kagonbe et al. (2021) for roofing tiles, except for the production of massive bricks
Figure 9. Variation of the water absorption capacity of the soils with firing temperature
Figure 10. Variation of the LOI of the soils with firing temperature
Figure 11. Variation of the flexural strength of the soils with firing temperature
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CONCLUSION
The mineralogical and physical analysis of clayey soils from selected sites in Ekiti State was conducted in this
study to assess their suitability as raw materials for ceramic production. Based on a comprehensive analysis, the
clays examined show significant potential for manufacturing common bricks, perforated bricks, and roofing tiles,
provided certain technical adjustments are made. The mineralogical composition revealed that the primary clay
minerals are kaolinite and illite, along with notable amounts of quartz, while muscovite and goethite are present
in substantial quantities. The high content of clay fractions, especially kaolinite and illite, in the absence of
smectite minerals, confirms these clays as suitable raw materials for high-quality ceramics. The considerable
presence of illite is particularly beneficial, as it enhances plasticity and promotes vitreous phase formation during
firing, thereby increasing the strength and density of the ceramic bodies. Illite-rich clays are commonly used as
fluxing agents in traditional ceramics to produce cooking pots, stoneware tiles, and bricks. Additionally, the
dominant presence of quartz as a non-clay mineral further strengthens the structural integrity and durability of
the final ceramic products. Physical characterization showed that the soils are made up of particles comprising
clays, silts, sand, and subordinate quantities of gravel. The clay-sized particles, less than 2µm, varied from 5.2
to 26%; samples from deeper depths had a higher percentage of clays. This range is advantageous as it suggests
that the raw materials when fired would not exhibit excessive shrinkage, because the materials with finer
fractions greater than 80% show excessive shrinkage. Based on the Winkler diagram, most of the studied clay
soils fall within common bricks, perforated bricks, roofing tiles, and masonry bricks, although Ire-1 may require
amendment before being used. The liquid limit values obtained from the Atterberg limits analysis ranged from
37.3 to 95%, plastic limits from 13.8 to 60.1%, and plasticity indices ranging between 19 and 42.6%. These
classifications using the plasticity chart place the soil within the medium to high plasticity and compressibility
region. Most of the samples had liquid limit values within the specified range for raw clayey materials meant for
ceramic purposes. It is interesting to note that all samples yielded plasticity indices well above 18.97%, as
compared to the threshold value of 10% below which materials are regarded as unsuitable for ceramic production
due to susceptibility to cracking during extrusion. Nevertheless, from the analysis of the workability chart,
samples Ire-2, Ire-3, Ara-2, and Isa-3 would need amelioration of their properties before processing due to their
linear shrinkage characteristics. Furthermore, samples Ire-2 and Isa-3 showed very high plasticity indices,
resulting in a sticky consistency; hence, they need to be amended. The linear shrinkage values varied between
8.6 and 20%, with an average of 13%, which exceeds the optimal range of 7 to 10% specified for fired clays.
These relatively high values linked to the clay content and the presence of illite may lead to deformation and
microcracking during brick production. For this reason, the use of degreasers is highly advisable to reduce
plasticity before its application, especially for samples whose linear shrinkage is higher than 15%.
Technological testing uncovered important links between firing temperature and ceramic properties. Water
absorption capacity decreased from 15.4-39% at 850°C to 10.44-15.42% at 1100°C, showing better densification
at higher temperatures due to combustion of organic matter, decarbonation, dehydration reactions, and the
formation of a glassy phase. At 1100°C, most samples achieved water absorption values within the maximum
limits of <25% for dense bricks and <20% for roofing tiles, as specified by Souza (2002); however, many of
these samples still exceeded those limits, making them unsuitable for such uses without further optimization. At
1000°C, water absorption ranged from 8.03 to 24.27%, meeting quality standards for structural ceramics.
Flexural strength increased steadily with higher firing temperatures, confirming that this property relies heavily
on temperature. Illite showed the strongest influence on the post-firing flexural strength of the studied samples.
Nonetheless, a key technical issue must be addressed: the flexural strength values at 1000°C were significantly
lower than those reported by Dondi et al. (2002) for Italian brick clays and Kagonbe et al. (2021) for roofing
tiles. At this temperature, the clays are only suitable for producing massive bricks. To reach flexural strength
levels that satisfy industry standards for high-quality roofing tiles and structural use, firing temperatures above
1000°C are necessary. Samples fired at 1100°C exhibited improved flexural strength, nearing acceptability for
broader ceramic applications; however, further optimization might still be needed for high-value products.
List of Abbreviations
FS flexural strength
LOI Loss on Ignition
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue XI November 2025
Page 896
www.rsisinternational.org
XRD X-ray diffraction
ICDD International Center for Diffraction Data
BSI British Standard Institution
ASTM American Standard for Testing Materials
LL liquid Limit
PL Plastic Limit
CL Clays of low plasticity
CI Clays of Intermediate plasticity
CH Clays of high plasticity
ML-OL
Organic clays and silt of low plasticity
MI-OH
Organic clays and silt of intermediate plasticity
MH-OH
Organic clays and silt of high plasticity
ACKNOWLEDGEMENTS
Not applicable
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